NASA Technical Memorandum 102546

Feasibility of Intercalated Graphite

Railgun Armatures

James R. Gaier

Lewis Research Center

Cleveland, Ohio

Clarence E. Gooden

Eglin Air Force Base

Fort Walton Beach, Florida

Doreen Yashan

Cleveland State University

Cleveland, Ohio

Steve Naud

Naval Coastal Systems Laboratory

Panama City, Florida

Prepared for the

5th Symposium on Electromagnetic Launch Technology

sponsored by the Institute of Electrical and Electronics Engineers

Fort Walton Beach, Florida, April 2-5, 1990

,l,_ li' I

Uric ] ,s

FEASIBILITY OF INTERCALATED GRAPHITE RAILGUN ARMATURES

James R. Gaier', Clarence E. Gooden", Doreen Yashan'", and Steve Naud ....

"NASA Lewis Research Center, Cleveland, OH 44135

"'E lin Air Force Base, Fort Walton Beach, FL 32542

"'_Cleveland State University, Cleveland, OH 44115

.... Naval Coastal Systems Laboratory, Panama City, FL 32407

Abst_et

Graphite intercalation compounds may provide an excellent

material for the fabrication of electro-magnetic railgun armatures.

As a pulse of power is fed into the armature the intercalate could

be excited into the plasma state around the edges of the

armature, while the bulk of the current would be carried through

the graphite block. Such an armature would have desirable

characteristics of both diffuse plasma armatures and bulk

conduction armatures. In addition, the highly anisotropic nature

of these materials could enable the electrical and thermal

conductivity to be tailored to meet the specific requirements of

electromagnetic railgun armatures. Preliminary investigations

have been performed in an attempt to determine the feasibility

of using graphite intercalation compounds as railgun armatures.

Issues of fabrication, resistivity, stability, and electrical current

spreading have been addressed for the case of highly oriented

pyrolytic graphite. This research was initiated and conducted as

part of AFATL's Electromagnetic Launcher Technology Program,

Site A-15, Eglin AFB FI.

lntroductio_

Electromagnetic launchers have been suggested as an

economical way to propel some payloads into space (especially

from the lunar surface) and as launchers for antiballistic missile

projectiles. Advancing the technology of electromagnetic

launchers has proved to be a continuous research and

developmental challenge. This challenge, in part, reflects the

complexities encountered when attempting to extract and apply

the physics of railgun armatures. Armatures, aside from having

to be compatible with projectiles and launchers, must maintain

electrical contact with the rails, conduct megaampere currents

during millisecond time frames, absorb and dissipate ohmic heat,

withstand kiloatmospheric pressures, and minimize in-bore

damage. Understanding of such fundamental issues such as arc

initiation, armature separation, current distribution, and arc

length with regard to the behavior and performance of armatures

remains ambiguous. Discussions of the four classical armature

types (solids, plasmas, hybrids, and transitioning) along with their

stringent requirements for developing hypervelocity railguns are

provided at length in numerous electromagnetic launcher reports

and publications. 1

It may prove fruitful to explore the feasibility of

fabricating armatures from graphite intercalation compounds

(GIC's). GICs are layered compounds with alternating layers of

aromatic carbon sheets (graphene planes) and guest atoms or

molecules (intercalates). The axial resistivity of GIC's can be

lower by an order of magnitude over pristine graphite with little

change in the mechanical properties. Of interest to the

development of armatures is their potential for transmitting high

and uniform electric currents from plasma armatures diffused in

the solid graphite host armature. In this way rail to solid

armature electrical contacts would be enhanced by the addition

of diffused plasma contacts.

With graphite as the host, elements such as lithium (Li) or

bromine (Br2) are diffused between the graphene planes which

creates a pattern of alternating layers with distinct electrical and

thermal properties. This pattern can be tailored because of a

phenomenon called staging. A fully intercalated (stage I)

compound has alternating graphene and intercalate layers. If half

of the intercalate is removed, the lattice collapses into a stage 2

compound, in which one intercalate layer alternates with two

graphene layers. Further dilution can produce stage 3, 4 and

even higher stages. Other tailorable parameters include the

crystallinity of the host graphite, and the choice of intercalate

molecule.

The feasibility of intercalated graphite railgun armatures

will depend upon the meeting of a hierarchy of objectives. The

first is the fabrication of GIC's of sufficient size and quality to

make a practical armature. The choice of intercalate must be

guided by its chemical stability and its capacity to transmit and

maintain high and uniform electrical currents. In addition, the

GIC armature must have sufficient elastic and tensile strength to

withstand the high pressures emanating from plasmas and J x B

forces, and to thermally dissipate hot plasma constituents without

losing the mechanical and thermal integrity of the armature.

This study is the initial phase of determining the feasibility

of GIC's as armature materials. Relatively large pieces of

graphite were intercalated with one of two candidate host

materials, Br 2or cadmium chloride (CdCI2). The dynamics of the

intercalation process were analyzed as a function of sample size,

and the intercalation compounds were characterized structurally

and electrically.

Methods and Materials

The graphite used for this study was "ZYH" grade of

highly oriented pyrolytic graphite (HOPG). This is a high purity

graphite with well oriented crystallographic "c" axis, and randomly

oriented, or turbostratic, "a" axis. Precession x-ray diffraction

photographs show the preferential ordering of the samples. In

the crystallographic hOl zone (Figure la) the structure is well

ordered (except in the h00 direction). In the hkO zone random

ordering gives rise to Debye rings in the diffraction pattern.

HOPG was intercalated with Br 2 using standard vaporphase techniques which have been described elsewhere 2. The

procedure and apparatus used to intercalate HOPG with CdCI2

has also be described in detail elsewhere 3.

In order to look at the scaling laws, pieces of HOPG with

sizes ranging from 2 x 5 x 10 mm to 8 x 10 x 50 mm were

intercalated with Br 2. (The smallest dimension is along the "c"

axis and undergoes expansion during intercalation.) The

intercalation and deintercalatlon rates were determined as well

as the amount of Br2 uptake. Deintercalation rates and densities

were also determined for HOPG intercalated with CdCI 2
ORIGINAL PAOF_

BLACK A_I.D _LH±T_£_i-iO_[_OG_AV_n

(a) PRISTINE. (b) BROMINE INTERCALATED. (c) CADMIUM CHLORIDE INTERCALATED.

FIGURE I. - X-RAY DIFFRACTIONHOI PRECESSIONPHOTOGRAPHSOF HOPG.

During the HOPG - Br, intercalation reactions, the "c"

axis expansions were monitored and analysed as a function of

sample size. When the expansion stopped, the reaction was

assumed to be completed,but the reaction chamber remained

sealed for an additional (_0 - 84 hours. The samples were then

removed from the reaction chamber, and their weight loss was

monitored. The expansion was not reversible so this was not

monitored.

It is difficult to characterize the electrical properties (such

as resistivity) of highly crystalline graphite because of the large

anisotropy between the "a" and "c" axes. Typically the resistivity

along the "a" axis of graphite is three orders of magnitude less

than the resistivity along the "c" axis. _ Thus, when making

measurements it is often difficult to determine whether the

current has spread throughout the bulk of the sample, or whether

only the top few layers are being measured. Intercalation

actually increases the anisotropy, and makes the measurements

even more difficult. _

The classical resistivity measurement technique utilizes a

four-point probe. The outer two contacts provide a constant

current to the sample, while the inner two sense the voltage drop.

If the in-plane ("a" axis) resistivity is to be measured, current

must be spread throughout the bulk of the material. Silver paint

is painted across the entire end of the sample. This provides a

current path to each of the graphene planes. The voltage probe

can then be placed on the surface. The current spreading is

enhanced if a rather long and thin piece of graphite is used.

Painting on a series of voltage contacts allows the construction of

a voltage-distance plot, and the least squares fit line will be a

more accurate value than that obtained from a single pair of

points.

If the voltage probes are mounted, not along the top of

the sample, but along the side, the same value for the resistivity

should be obtained. A comparison between these two values will

reveal how successfully the current has been spread throughout

the sample.

The transverse resistivity (along the "c" axis) is also an

important value. Since no current flow is desired in that

direction, a large transverse resistivity has advantages. To

measure the transverse resistivity the voltage probes are first

attached to the top and bottom faces of the sample. To facilitate

even current spreading throughout, the top and bottom faces are

painted with silver paint, except for the areas where the voltage

leads are attached. The current leads are then attached to the

painted faces.

The problem of anisotropy can be side-stepped if the

contactless rf eddy current technique is used. A radio frequency

field (in our case 55.55 kHz) set up across the sample induces

eddy currents. The additional current which must be added to

maintain the amplitude of the rf field is proportional to the

resistivity and the thickness of the sample. No contacts need to

be made, and only the component perpendicular to the magnetic

field (the "a" axis) is affected. One drawback to this technique is

that rather wide samples (at least a 2 cm square) are required to

minimize edge effects. The rf resistivity of the individual samples

could not be measured due to this constraint, but it was measured

on some rather large pristine samples.

In some respects the absolute resistivity is not important

in a railgun armature application. What is important is the

"effective resistivity" in the railgun configuration. This includes

resistiviw along the axis between the rails, and the contact

resistance between the armature and the rail. Thus, a two-point

resistance railgun test apparatus was constructed which duplicates

the electrical environment the sample will be subjected to.

Results and Discussion

One measure of the quality of the HOPG is its density.

Graphite has a crystallographic density, of 2.2556 g/cm 3. The

density of real samples, however, is lowered by an amount which

is dependent upon the number of defects. Hence, the more

perfect the crystallinity of the sample, higher is its density. The

density was determined by measuring the linear dimensions with

a digital caliper, and weighing the samples on an analytical

balance. Although this method is not particularly accurate, it has

the advantage of being non-destructive and non-contaminating.

The average density of the pristine graphite was measured to be

2.22 _+ .03 g/cm 3. :The rather large scatter (1.4 percent) is due

principally to the fact that the surface was not smooth but

exhibited "bubble" structures. There may also have been errors

in measuring the linear dimensions, and in the squareness of the

corners of the sample.

Bromine Intercalation

The progress of the Br2 intercalation reaction was

monitored via expansion along the "c" axis direction. The

thickness of the largest sample was measured at regular intervals

throughout the reaction until it was constant. An example of the
first two hours of a reaction is shown in Figure 2. Note that

there is no change in the thickness during the first five minutes.

During this time the vapor pressure of the Br 2 is increasing as it

evaporates from the reservoir. Once a threshold pressure of Br 2

is built up, the reaction begins. The majority of the expansion

occurs within the first two hours, but it continues at a low rate for

several hours afterwards. Eventually, large cracks appear

between the graphene planes within the sample, and bending

distortions appear. This casts doubt on the value of using

expansion to monitor the reaction in its later stages. After about

80 hours the reaction was assumed to be complete.

1.8--

==

-- 1,6--

=

1.q--

_o 1.?--

_ 1.0----"

0

0

I I t I I I

20 qO 60 80 100 120

TIME, MZN

FIGURE2. - EXPANSIONIN THECRYSTALLOGRAPHIC "C"

DIRECTIONOf"ItOPGUPONEXPOSURETO 165 IORROF

BRORINE VAPOR.

It has been shown by several authors that Br 2 rapidly

diffuses out of graphite when the sample is removed from the Br 2

atmosphere. In order to obtain the maximum amount of Br 2

intercalated into the graphite, samples were rushed from the

reaction chamber to tared weighing bottled and quickly sealed.

The weight uptake of Br z by samples of various sizes is shown in

Table I. From the weight uptake the nominal stoichiometric

formula and nominal stage of the intercalation compound can be

determined. These are also shown in Table I.

The data depicted in Table I reveal that there was a large

effect of sample size on the uptake of Br 2 by the graphite. There

are two possible interpretations for this effect. The Br 2 might be

taken up more quickly by smaller pieces of graphite, especially if

it is a diffusion controlled reaction. Alternately, the Br 2 may be

lost more quickly by larger pieces, perhaps because larger stresses

cause larger cracks and so more avenues of escape. The

weighing bottles were opened and the Br 2 allowed to escape. At

periodic intervals the sample vials were again weighed. In this

way the deintercalation reaction was monitored. As can be

clearly seen in Figure 3, smaller pieces, not larger, delntercalate

more rapidly. This is consistent with a diffusion controlled

deintercalation reaction.

This points to a diffusion controlled intercalation reacti.n

also. The larger pieces (perhaps even the smallest pieces)

probably did not have sufficient time to fully react. The

macroscopic cracks in the sample may have masked microscopic

expansion. It is possible that large pieces cannot be intercalated

within a reasonable reaction time. There are cases in the

literature of intercalation reactions which took months to go to

completion, ln-situ weight measurements, which are being

undertaken at this time, are needed to answer these questions.

L9

,+1

.98 --

.g& --

.9q --

.92

o _Ox10

10x10

o 5x10

o lx10

o

[3

0 /3. _ 0 0 []

A

0

0

0

I I I i I I i I

.05 .I0 .15 .20 .25 .30 .35 .lJO

TIME INAIR, DAYS

FIGURE3. - WEIGHTLOSSOF VARIOUSSIZE SARPLESOf

SAMPLESOF BRORINEINTERCALATEDHOPGOVER TIME.

X-ray diffraction precession photographs confirmed that

there are regions of Br 2 graphite intercalation compounds even

in samples that had been allowed to desorb for several weeks

(Figure lb).

The rapid deintercalation of the Br 2 from the IlOPG

points to a larger issue, that of stability. It appears as though

large stockpiles of Br 2 intercalated graphite armatures could not

be manufactured in advance and stored until use. Not only

would a large portion of the intercalate diffuse out, returning the

graphite to its near pristine state, but the constant outgassing of

corrosive and toxic Br 2 would pose an environmental hazard.

However, Br 2 intercalated graphite armatures could be stored in

sealed containers, to be opened only just before loading. In the

early stages of deintercalation, the reaction may even be

sufficient to provide a local atmosphere of easily ionized gas

which could aid the initiation stage of firing the railgun.

Table I - Sample Characteristics of Brz Intercalated ZYH Grade Highly Oriented Pyrolytic Graphite

Length Width Height Vol me Mass Density S/_. Mess Br Nominal Nominal

cm cm cm cm_u qram q/cm ° cm"1 aram Formula Stlqe

1.015 .146 .616 .912 ,2068 2.2675 18.9 .3743 Cs.2Br 1.2

1.057 .519 .240 .132 .2890 2.1960 14.1 .4453 C123Br 1.8

1.027 1.008 .268 .277 ,6069 2.1910 11.4 ,8936 C14.1Br 2.0

2.727 1.091 .283 .841 1.8676 2.2204 9.64 2.4658 C20.8Br 3.0

5.055 ,971 .614 3.013 6.7100 2.2274 5.71 7.8917 C3r.sBr 5.4
Cadmium Chloride Intercalation

There are enough safety and storage concerns with Br_

intercalated HOPG to make it prudent to consider a more stable

intercalate. CdClz intercalated graphite fibers have been

reported to be stable compounds. 6'3 Thus, several small pieces of

CdCI 2 intercalated ZYH grade HOPG were produced as a

possible alternative.

Table I1 shows the sample characteristics of the graphite

intercalated with CdCI 2. The linear dimensions are not as well

characterized as the Br 2 intercalation samples were, and that may

be reflected in the pristine density measurements, which were

quite low (2.17 _+ .1)2 g/cm3). The reaction conditions required

to intercalate a sample with CdCI 2 are much more severe than

those required for Br 2 intercalation, but the higher surface to

volume ratios were thought to help ensure the reaction would go

to completion. Unfortunately, from the mass uptake data it is

evident that the reaction was far from completion even in the

case of the smallest sample sizes. X-ray diffraction precession

photographs of CdCI 2 product show that graphite intercalation

compounds are fl_rmed (Figure lc). The vertical streaks that

appear between the graphite reflections are due to disordered

CdCI 2 located between the graphene planes. These results

indicate that there are areas of well staged graphite, so evidently

the samples are not homogeneous.

__ 1.o, -

 1.o2 °

_-_ 1.00

0

CUBE.

mm

o 3.0

3.8

t_ q,G

o 5.3

0 0 0 0 0 0

a

o i i i o

5 10 15 20 25

TIRE, DAYS

I

30

FIGURE q. - DEGRADATION OF VARIOUS SIZE SAI_LES OF

CADRIUR CHLORIDE INTERCALAIED HOP6 OVER lllff_.

the best intercalate from a performance standpoint. It also,

however, makes very unstable intercalation compounds, and so

poses some possible problems.

Sodium hydride (Nail) may also offer low ionization

potential and light weight. Nail also forms relatively stable

GIC's, so this may be a compromise compound that combines

low ionization potential with ambient condition chemical stability.

Table II -- Sample Characteristics of CdCI2 Intercalated ZYH Grade Highly Oriented Pyrolytic

Graphite

Length Width Height Vol me Mass Density S/V Mass Cd Nominal

.cm (;:m (;:m cm_u aram o/Gm" _:m"_ aram Formu n-

.305 .305 .305 .0283 .0614 2.1690 64.6 .0738 CroCdCI2

.301 .381 .38t .0553 .1210 2.1878 41.3 .1347 C135CDCI2

.457 .457 .457 .0956 .2104 2.2015 28.7 .2194 C36oCdC12

.533 .533 .533 .1518 .3318 2.1863 21.1 .3658 CtsoCdCI2

4.064 .305 .305 .3776 .8168 2.1634 24.8 .8689 C24oCdCI2

4.064 .381 .381 .5899 1.269 2.1511 18.4 1.341 C2;,oCdCI2

4.064 .457 .457 .8495 1.639 2.1648 11.7 1.955 C24oCdCI2

4.064 .533 .533 1.1563 2,481 2.1457 8.9 2.636 C24oCdCI2

The stability of the weight of these compounds was

considerably higher that the Br 2 compounds as can be seen in

Figure 4. Whereas the weight dropped in the case of Br 2

compounds as Br 2 diffused from the lattice, the weight increases

over time for the CdCI 2 intercalated samples. If generalizations

can be made from CdCI z intercalation compounds with fibers as

the host, this is due to the uptake of water. In graphite fibers the

weight increase can be accelerated by putting the samples in a

high humidity environment, and can be reversed by heating.

Other Intercalates

There are, of course, considerations which may over-ride

the stability issue. An important performance characteristic may

well be a low ionization potential for the intercalate. We are

initiating a program to study the dynamics of intercalation with

Li. Li, with its light weight and low ionization potential may be

Electrical Propcrti¢_

The principal reason to intercalate graphite for railgun

armatures is to decrease the resistance of the armature. Perhaps

the largest gain wilt be in the lowering of the contact resistance,

but the bulk resistivity of the material is also lowered.

Intercalation provides additional charge carriers (electrons in the

case of Li and Nail, holes in the case of Br 2 and CdCI_) in the

conduction band. "A" axis resistivity can be lowered by several

orders of magnitude over pristine graphite)

The values of the axial resistivity (measured along the "a"

axis) the transverse resistivity, the eddy current resistivity, and the

resistivity in the railgun configuration are summarized in "l'able

I11. There are several clues in this table that the current

spreading was not uniform in these samples, and that the

resistivity values are indeed maximum values.
Report Documentation Page National Aeronautics and

Space Adrnmistrallon

1. Report No. 2. Government Accession No, 3. Recipient's Catalog No.

NASA TM- 102546

4. Title and Subtitle 5. Report Date

Feasibility of Intercalated Graphite Railgun Armatures

7. Author(s)

James R. Gaier, Clarence E. Gooden, Doreen Yashan, and Steven Naud

9. Performing Organization Name and Address

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, D.C. 20546-0001

6. Performing Organization Code

8. Performing Organization Report No.

E-5332

10. Work Unit No.

506-41-41

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Memorandum

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared for the 5th Symposium on Electromagnetic Launch Technology, sponsored by the Institute of Electrical

and Electronics Engineers, Fort Walton Beach, Florida, April 2-5, 1990. James R. Gaier, NASA Lewis Research

Center. Clarence E. Gooden, Eglin Air Force Base, Fort Walton Beach, Florida 32542. Doreen Yashan,

Cleveland State University, Cleveland, Ohio 44115. Steve Naud, Naval Coastal Systems Laboratory, Panama

City, Florida 32407.

16. Abstract

Graphite intercalation compounds may provide an excellent material for the fabrication of electro-magnetic railgun

armatures. As a pulse of power is fed into the armature the intercalate could be excited into the plasma state

around the edges of the armature, while the bulk of the current would be carried through the graphite block.

Such an armature would have desirable characteristics of both diffuse plasma armatures and bulk conduction

armatures. In addition, the highly anisotropic nature of these materials could enable the electrical and thermal

conductivity to be tailored to meet the specific requirements of electromagnetic railgun armatures. Preliminary

investigations have been performed in an attempt to determine the feasibility of using graphite intercalation

compounds as railgun armatures. Issues of fabrication, resistivity, stability, and electrical current spreading have ......

been addressed for the case of highly oriented pyrolytic graphite. Thi_ research was initiated and conducted as

part of AFATL's Electromagnetic Launcher Technology Program, Site A-15, Eglin AFB FI.

17. Key Words (Suggested by Author(s))

Graphite intercalation compounds

Electromagnetic railguns

Railgun armatures

18. Distribution Statement

Unclassified- Unlimited

Subject Category 27

19, Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages

Unclassified Unclassified 6

NASAFORM1626OCT86 *For sale by the National Technical Information Service, Springfield, Virginia 22161

22. Price"

A02
Table III -- Resistivity of ZYH Grade HOPG

Resistivity Pristine Br..2 CdCI2

mfl-cm ZYH Infercalated Intercalated

Axial 0.600 0.690 0.100

Transverse 13. 7.4 100.

RF Eddy 0.500 .........

Current

Reilgun 180,000 1,400 ....

Other possible alternatives include using lithium or sodium

hydride graphite intercalation compounds, which are expected to

perform very well in the plasma state.

Acknowledeements

The authors would like to thank P.D. Hambourger of Cleveland

State University for his help with the electrical characterization

of the samples. This research was initiated and conducted as part

of AFATL's Electromagnetic Launcher Technology Program, Site

A-15, Eglin AFB FI.

The "a" axis resistivity for the large samples we measured

is about an order of magnitude higher than values reported in the

literature 3. When very thin samples of pristine ZYH were

measured, values similar to those in the literature (40 _fl-cm)

were found. The rf eddy current value, however, is quite close to

the axial resistivity measured on the large samples. This is

difficult to explain.

The transverse resistivity values are more consistent with

literature values. 4 The path of the current in this direction,

however, is much more resistive than in the perpendicular

directions (along the "a" axes) so spreading of the current is not

expected to be as much of a problem. Each plane will tend to be

an equipotential surface. As was discussed earlier, intercalation

causes an expansion along the transverse ("c" axis) direction. This

results in poor crystallite-to-crystallite contacts in this direction

and so a wide sample-to-sample spread in the transverse

resistivity for intercalated ZYH.

The raitgun resistivity is much higher, and that is to be

expected. This is because it includes the sample to rail contact

resistance in addition to the sample resistance. The contact

resistance term totally dominates the measured resistivity.

Herein lies the hope of this armature design. When the plasma

is activated, it will make contact between the sample and the rail.

The additional current path should substantially reduce the

contact resistance which will substantially reduce the railgun

resistivity.

References

1. L.D. Thornhill and J.H. Batteh, IEEE Transactions on

Magnetics 25, (1989) p. 552.

2. J.R. Gaier, Synthetic Metals 22, (1987) p. 15.

3. C.E. Gooden, C. Pham, S. Naud, and J.R. Gaier, J. Appl. Phys.

64, (1988) p. 2384.

4. D. Marchand, C. Fretigny, M. Lagues, A.P. Legrand, E.

McRae, J.F. Mareche, and M. Lelaurain, Carbon 22 (1984)

p. 497.

5. A.R. Ubbeiohde, Proc. R. Soc. London, Ser. A, 327 (1972) p.

289.

6. D.D. Domingues, A.W. Saunders, R.M. Panayappan, and J.S.

Murday, Extended Abstracts of the Symposium on Graphite

Intercalation Compounds, edited by P.C. Eklund, M.S.

Dresselhaus, and G. Dresselhaus (Materials Research

Society, Pittsburgh, PA, 1984) p. 214.

Conclusion_

Before railgun tests can proceed with an intercalated

graphite armature, there are several parameters which must be

optimized. If the Br 2 intercalation compound is to be used, then

reaction rates must be increased, or reaction times must be

lengthened. The rate might be increased by lowering the

temperature of reaction. This technique has allowed poorly

graphitized fibers, such as Amoco P-55, to be brominated,

something which was not possible at room temperature. In-situ

evaluation is required to know when the reaction has come to

completion.

Both the intercalation and deintercalation reactions appear

to be diffusion controlled. While this means that the

intercalation reaction may be more time consuming when using

larger samples, it also means that there will be a larger open air

shelf life. The shelf life will still probably be short, and the

armatures should remain sealed until just prior to use.

There are advantages to using CdCI 2 as the intercalate, but

disadvantages also. The principal advantage is in its stability and

ease of handling after manufacture. Disadvantages include a

much more complex fabrication process, and perhaps somewhat

lower performance in the railgun due to its higher ionization

energy.

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Space Administration

Lewis Research Center

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